(1) Field of the Invention
This invention relates to an easily finger-tearable polyolefin laminated film. More particularly, the present invention relates to a multi-layered polyolefin laminated film which is easily finger-tearable and excellent in practical strength and is devoid of such drawbacks as curling, whitening when torn, fibrillation, and so forth.
(2) Description of the Prior Art
Various methods of producing a polyolefin film having excellent finger-tearability have been proposed in the past such as a method which laminates a uniaxially oriented film (hereinafter referred to as a "UO film") oriented in the transverse direction on a biaxially oriented film (hereinafter referred to as a "BO film") (e.g., U.S. Pat. No. 3,887,745), a method which radiates radioactive rays such as electron beams to the BO film (e.g., Japanese Patent Application Laid-Open No. 106779/1978), a method which interposes a thermoplastic resin layer having a second order transition point of 40.degree. to 130.degree. C. and elongation at tensile break at 20.degree. C. of up to 30%, such as of polystyrene and polymethacrylic acid alkyl ester polymers, between two polypropylene layers (e.g., Japanese Patent Application Laid-Open No. 28814/1980), and so forth. The laminated films thus produced are used for an adhesive tape, for packaging flowers and other applications where finger-tearability is required. However, these laminated films have the following drawbacks. In the case of the laminated film consisting of the BO/UO films, the film gets turbid and undergoes whitening when cut. The cut portion partially remains unremoved and miscut is likely to occur. When heated to 40.degree. to 50.degree. C., the laminated film substantially loses finger-tearability and has a tendency to curl. In addition, the productivity of the film is low. In the case of the electron beam radiation method, the resulting laminated film fails to satisfy the requirements of finger-tearability and toughness. Even if the film has finger-tearability, the surface layer of the film is likely to undergo cleavage. The three-layered film interposing the polystyrene or polymethacrylate layer between the two polypropylene layers involves the drawbacks of low adhesion between these layers, easy cleavage, low transparency and low resistance both to chemicals and heat. Moreover, since the waste can not be recovered during the film manufacturing process, the productivity of the film is also low.